Time Fences – points in time that separate phases of a master
schedule planning
horizon.
o MPS schedules can be viewed as being divided into three
sections, each section that is called a time fence.
• The first is referred to as frozen. Frozen means that
MPS cannot be changed.
• The next is referred to as firm. Firm means that
changes can occur in this section. Available production
capacity has been allocated to orders. Change this
section can be made cost (slightly affected)
• The last is referred to as open. Open means that not all
the production capacity has been allocated, new orders
are ordinarily slotted.